trachybasalt

views updated

trachybasalt The fine-grained, extrusive equivalent of syenogabbro. When undersaturated, feldspathoidal minerals take the place of alkali feldspar to generate feldspathoidal trachybasalts known as tephrites (olivine-free) and basanites (olivine present). Trachybasalts are found on the stable continental crust and on some oceanic islands.

More From encyclopedia.com